Lesser scaup description

One of the most abundant and widespread of North American ducks, the lesser scaup (Aythya affinis) is a medium-sized, black and white diving duck with a slight crest (2). For much of the year this species displays sexual dimorphism. The male is characterised by its black head with a purplish gloss, as well as by its black neck and breast, white flanks and belly, and grey-flecked lower mantle. The female is chocolate brown, with grey-flecked wing-coverts and a white patch at the base of the dark grey bill. The iris of the male is brilliant yellow, but in the female it is olive-brown to brownish-yellow (3)(4).

The lesser scaup is very similar in appearance to its close relative, the greater scaup (Aythya marila). However, the lesser scaup may be distinguished by its smaller, more delicate head, steeper forehead and thinner, narrower bill (3)(5). The female lesser scaup also has less white at the base of the bill (2).

Related species

Lesser scaup biology

An excellent swimmer and diver, the lesser scaup feeds mostly by diving in shallow water, where it feeds on aquatic plants or invertebrates(2)(3). It will dive to a maximum depth of around 8 metres, with each dive lasting about 30 seconds, interspersed with surface intervals of 10 to 12 seconds (6). The lesser scaup will also sometimes feed at the water's surface, either by grabbing food items from the surface or by dipping its head and neck below the water (7).

Generally gregarious throughout the year, the lesser scaup forms breeding pairs at stopover points during migration. The male initiates courtship with head throws, shakes, sneaking behaviour and turning the head back, followed by mutual preening behind the wing and cough-like movements with a whistled sound (6). Nesting begins in May or June, when a shallow nest is created on the ground among thick vegetation and lined with plant matter. Between 9 and 11 eggs are laid, and are incubated by the female for 21 or 22 days (2). The male lesser scaup usually abandons the female halfway through the incubation period to fly to moulting areas, where the male begins a flightless period (6).

Soon after the chicks hatch, the female lesser scaup leads them to water, where they feed themselves on invertebrates amongst emergent vegetation (6). The ducklings are able to dive at just 2 days old (6), and are able to fly at 45 to 50 days (2). The lesser scaup reaches maturity at one to two years of age, and the oldest known individual was ten years old (2).

Lesser scaup range

The lesser scaup breeds throughout much of the interior of Alaska and Canada, south to California, Nevada, South Dakota and Minnesota in the United States. The northern limit of its breeding range is the open boreal forest and forest tundra of Alaska, Yukon and the Canadian Northwest Territories (3).

A migratory species, the lesser scaup winters mainly along the Louisiana and Florida Gulf Coasts, as well as on Lake Okeechobee in Florida and along the Pacific and Gulf Coasts of Mexico. It may also be commonly found along the southeast coast of Alaska, in northwest California, around the Great Lakes and along the upper Atlantic coast of the U.S. The southern limits of its winter range include southern Mexico, occasionally as far south as northern South America, and most islands in the Caribbean region, from the Bahamas, Cuba and Jamaica, east to Nevis (3).

Species with a similar range

Lesser scaup habitat

The lesser scaup usually nests in areas near fresh to moderately brackish water, in seasonal or semi-permanent wetlands and lakes with much emergent vegetation. The nest is constructed on the ground amongst tall vegetation, often in upland areas away from water. At other times of the year, the lesser scaup occupies a variety of aquatic habitats, including coastal lakes, reservoirs, bays and estuaries (3).

Lesser scaup status

Lesser scaup threats

Although the lesser scaup is the most abundant diving duck in North America, its population has been in decline since 1985. The exact cause of this is unclear, but it is likely to be due to a number of threats, including habitat degradation and poisoning (4).

In Florida, for example, much lesser scaup habitat has been lost or degraded as a result of drainage, dredging, filling, and extensive modification of water levels by canal construction. Wetlands used by this species along Lake Erie and the Detroit River have also suffered from siltation, landfill, exotic plant introductions, and water level controls, while new logging practices in Canadian boreal forests may threaten the lesser scaup’s breeding habitat. In addition, the declining number of lesser scaups on the Illinois River, is possibly the result of the loss of prey due to sedimentation and altered water levels, as well as pollution (3).

Other threats to the lesser scaup include DDT, lead poisoning, and drought in prairie parklands, which may affect the ability of migrating females to store enough nutrients for successful breeding (3)(6). The lesser scaup is also a popular game species in the north-central U.S. (3).

Lesser scaup conservation

The North American Waterfowl Management Plan has coordinated the protection and restoration of much lesser scaup habitat, in cooperation with government agencies, private landowners and conservation organisations. However, most activities have focused on prairie parklands with little work in the boreal forests where the lesser scaup breeds (3).

The lesser scaup has benefited from harvest restrictions implemented between 1988 and 1998 which, along with declining numbers of hunters, have greatly reduced the harvest of this species (3).

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